In order to drill an oil or gas well, it is well-known to mount a drill bit at the bottom end of a line of drill pipe, commonly known as a drill string, and to rotate the drill bit and drill string into the earth in order to drill a borehole. Typically, a drill bit consists of a drill body which supports cone-type cutters which are rotated by the rotation of the drill string in order to cause the bits to grind and cut through the earth's formations. The grinding and cutting action of the drill bit creates drill cuttings which have to be removed from the bottom of the borehole so that the drill bit can continue its grinding and cutting without bogging down. In order to remove such drill cuttings, to clean and cool the drill bits, and for other reasons, it is known to circulate a drilling fluid, commonly known as "mud", downwardly through the drill string and outwardly of the drill bit with the fluid circulating upwardly in the annular area between the drill string and the borehole walls thus returning to the earth's surface. Upon return to the earth's surface, the drilling fluid is cleaned for re-circulation.
The importance of efficient removal of the drill cuttings cannot be over emphasized. Without efficient removal of the cuttings, the drill bit tends to re-grind the drill cuttings and thus lose efficiency. Efficiency of operation of the drill bit is directly proportional to the effectiveness of the removal of drill cuttings.
A number of attempts have been made to enhance removal of drill cuttings. U.S. Pat. No. 3,216,514 of Nelson discloses a rotary drilling apparatus having a valve means in the drill bit housing which is rotated in response to rotation of the drill bit cones due to the mechanical interconnection between the drill bit cones and the valve means. The valve means opens and closes passageways in the drill bit body in order to, as is taught in the patent, interrupt flow of fluid in the bit in order to cause a sudden downward force or water hammer effect to be exerted on the bit to increase the pressure of cutters on the formation and to reduce the hydrostatic pressure exerted by the fluid on the formation whereby the cuttings will be more readily broken away from the formation and entrained in the drilling fluid to be carried upwardly through the annulus. U.S. Pat. No. 4,114,705 of Milan discloses a drill bit utilizing two opposed pulsed jets 180.degree. out of phase which is achieved by utilizing a pivotally mounted ball which oscillates between two positions to respectively close off one of two outlet ducts leading to the nozzles to produce alternating pulsed flow. U.S. Pat. No. 3,897,836 of Hall and Clipp discloses the utilization of a hammer and piston internally mounted in a housing above the drill bit to cause continuously supplied compressed air to cyclically operate the hammer and piston to create a pulsed jet of water. Other attempts to enhance the removal of drill cuttings include the use of nozzles having certain flow restriction characteristics and extended tubes extending downwardly from the bit housing to enhance cross flow. It has also been taught to combine extended nozzles with return conduits to enhance cross flow.
Further, general fluid flow technology teaches that a sudden halt to fluid flow, for example, in a pipe by the closing of a valve, can cause a rise in pressure and creation of pressure waves that travel upstream to reverberate off of any reflecting surface, and are commonly known as hydraulic transients.
While many attempts have therefore been made to enhance circulation of drilling fluid outwardly of the drill bit in order to remove drill cuttings, it is believed that the state of the art may yet be improved.